Aneurysmal bone cyst (ABC) is an uncommon pathological condition, which leads to weakening and fracture of the affected part of the bone. Radiologically, ABC is an eccentric, metaphyseal, expansile, lytic and non-neoplastic lesion of the bone, giving blown-out/ballooned/soap-bubble appearance. Though benign, malignant transformation is reported. It accounts for 1–6% of all primary bone tumours with incidence rate of 0.14% annually. Usually occurs during second decade of life and most common sites for the lesions are the tibia, femur, vertebra, pelvis, humerus and fibula. The various treatment modalities include selective arterial embolisation, en-bloc/wide marginal resection and curettage with phenol, liquid nitrogen, etc., use of sclerosing agents and use of autogenic/allogenic bone graft or polymethylmethacrylate, with or without osteosynthesis. There exists controversy regarding optimum treatment of ABC as recurrence rate ranges from 5–40% depending upon the treatment method used. Use of non-vascularised fibular strut graft yields good results as per many studies especially in large lesions. Hereby, we present four cases of ABC, treated by extended curettage or En bloc excision of lesions and reconstruction using fibular strut graft.

Aneurysmal bone cyst (ABC) is an uncommon pathological condition, which leads to weakening and fracture of the affected part of the bone.[1] Radiologically, ABC is an eccentric, metaphyseal, expansile, lytic, and nonneoplastic lesion of the bone, giving blown-out/ballooned/soap bubble appearance.[2] Though benign, malignant transformation is reported.[3] It accounts for 1%–6% of all primary bone tumors, with incidence rate of 0.14% annually.[4] It usually occurs during the second decade of life and the most common sites for the lesions are the tibia, femur, vertebra, pelvis, humerus, and fibula.[5]

The various treatment modalities include selective arterial embolization, en bloc/wide marginal resection and curettage with phenol, liquid nitrogen, etc., use of sclerosing agents, and use of autogenic/allogenic bone graft or polymethylmethacrylate (PMMA), with or without osteosynthesis.[6] There exists controversy regarding the optimum treatment of ABC as recurrence rate ranges from 5% to 40% depending on the treatment method used.[7]

Use of nonvascularized fibular strut graft yields good results as per many studies, especially in large lesions.[8] Hereby, we present four cases of ABC, treated by extended curettage or en bloc excision of lesions and reconstruction using fibular strut graft.

Materials and Methods

The study included four patients (2 males and 2 females) diagnosed with ABC, with lesions at different sites with an average age of 18.75 years. Depending on the size and site of the lesions, under appropriate anesthesia, the lesions were treated by extended curettage or en bloc resection and nonvascularized fibular strut grafting. The length of the required fibula for bridging the bone defect was estimated radiographically. After resection of the cyst, the fibular strut graft was harvested by a lateral skin incision over the middle of the fibula. After that, exposure of the middle of the fibula was performed subperiosteally and the appropriate size of fibula was harvested by osteotomy. This fibula graft was incorporated in the cavity. Care was taken to preserve >5 cm of the proximal and distal portions of fibula to ensure stability of the knee and ankle. The periosteum was closed in children to facilitate fibular regeneration, and the wound was closed in layers without drainage and then dressed.

Case Reports

Case 1

A 12-year-old male child presented with pain and swelling over dorsum of the right foot, gradually increasing for 6 months. He used to walk with a limp on the affected side. Swelling was solitary, localized to the dorsum of the foot, firm in consistency, tender, about 6 cm × 4 cm, with irregular surface, and nonpulsatile without distal neurovascular deficit. On plain radiographs [Figure 1]a, expansile lytic lesion was evident on the 2nd metatarsal bone of the right foot. Magnetic resonance imaging (MRI) scan [Figure 1]a showed fluid-filled cavity, highly suggestive of ABC, and biopsy confirmed the diagnosis of ABC. The patient was operated with en bloc resection, excision of articular cartilage of proximal phalanx, and arthrodesis of the 2nd metacarpo-phalangeal joint with nonvascular fibular grafting which was stabilized using K-wires [Figure 1]b. Post operatively, the patient was immobilized in a below-knee cast for 2 months. After 4 months postoperatively, K-wire was removed as the graft got incorporated. At final follow-up, the patient had good functional recovery with no signs of recurrence [Figure 1]c.

A 25-year-old male presented with pain and swelling over the left lower leg, gradually increasing for 1 year. Ankle range of movement was painful and the patient was not able to bear weight on the affected leg for 2 months. Swelling was solitary, localized to the medial aspect of the lower leg, tender, firm in consistency, about 10 cm × 5 cm, with irregular surface, nonpulsatile, and without distal neurovascular deficit. On plain radiographs [Figure 2]a, expansile lytic lesion was evident on the left distal tibial metaphyseal region. Computed tomography (CT) scan [Figure 2]a showed cavity within the distal aspect of tibia, suggestive of ABC and biopsy confirmed the diagnosis of ABC. The patient was operated with curettage and phenol cauterization, and the cavity was packed with nonvascular fibular strut graft along with cancellous autograft taken from ipsilateral iliac crest [Figure 2]b. Postoperatively, the patient was immobilized in the above-knee cast for 3 months. After 5 months, the patient was allowed full weightbearing, as graft got incorporated within the cavity [Figure 2]c. At final follow-up, the patient had good functional recovery with normal range of movements and no sign of recurrence [Figure 2]d.

A 26-year-old female presented with pain and swelling over the left lower thigh and knee joint for 8 months. Knee range of movements was painful, and the patient was not able to walk since a month. Swelling was solitary, firm in consistency, localized to lateral aspect of the lower thigh, tender, about 10 cm × 5 cm × 4.5 cm, with irregular surface, nonpulsatile, and without distal neurovascular deficit. On plain radiographs [Figure 3]a, expansile lytic lesion was evident on the left distal femur metaphyseal region. MRI scan showed fluid-filled cavity, highly suggestive of ABC and biopsy confirmed the diagnosis. The patient was operated with curettage and chemical cauterization with phenol, and the cavity was packed with nonvascular fibular strut graft and osteosynthesis was done by internal fixation with condylar buttress plate [Figure 3]b. Postoperatively, the patient was immobilized in an above-knee cast for 3 months. After 6 months, the patient was allowed full weightbearing after graft got incorporated within the cavity confirmed by radiographs [Figure 3]c. At final follow-up, the patient had good functional recovery with normal range of movements and no sign of recurrence [Figure 3]d.

A 12-year-old female child presented with pain and swelling over dorsum of the left foot, which was gradually increasing for the last 4 months. The child walked with limp on the affected side. Swelling was solitary, firm in consistency, localized to dorso-lateral aspect of the midfoot, tender, about 2.5 cm × 2.5 cm, with irregular surface, nonpulsatile, and without distal neurovascular deficit. On plain radiograph, expansile lytic lesion was evident involving the entire cuboid and extending into the calcaneocuboid joint. CT scan showed [Figure 4]a cystic cavity in the cuboid bone suggestive of ABC and biopsy confirmed the diagnosis of ABC. The patient was operated with en bloc resection and arthrodesis at the 4th metatarsal and calcaneus using two nonvascularized fibular strut grafts [Figure 4]b. Postoperatively, the patient was immobilized in a below-knee cast for 2 months and later was allowed ankle motion exercises. After 4 months, the patient was allowed weightbearing as graft got incorporated. At the final follow-up, the patient had good functional recovery with normal range of movements and no sign of recurrence [Figure 4]c.

The average age of four cases ranging from 12 to 26 years is 18.75 years. Osteosynthesis was done in only two cases, one with distal femur and another with the 2nd metatarsal case. Fibular strut graft was incorporated within the cavity in all the four cases with an average time of 5 months. All cases had an excellent functional outcome. We had superficial infection in one case of distal tibia which subsided after 12 days. None of the cases showed recurrence till the final follow-up [Table 1].

Table 1: Details of four patients with aneurysmal bone cysts with various parameters

In 1942, the lesion is aneurysmal bone cyst was first described and defined by Jaffe and Lichtenstein and came to be known as Jaffe–Lichtenstein disease.[9] The exact etio-pathogenesis is uncertain. There are many theories such as posttraumatic bony alteration, reactive vascular malformation, and genetic predisposition.[10] The cavities are blood-/fluid-filled spaces of variable sizes separated by connective tissue septa containing osteoid and osteoclastic giant cells.[10] Usual presentation with ABC is mild-to-moderate pain, presenting for weeks to several months with firm and gradually enlarging mass in adolescents and occasionally pathological fractures.[11]

Radiographically, it is an expansile lytic lesion, which balloons out and elevates the periosteum but remains contained in a cavity formed by a thin shell of cortical bone, giving a cystic appearance. ABCs are mostly metaphyseal lesions, located eccentrically and sometimes centrically. CT is helpful in delineating the cyst in areas of complex anatomy with fluid-filled levels.[12] MRI is helpful in identifying multiloculated cavities along with its expansion into the surrounding soft tissues, fluid levels as well as blood within the cavity.[13]

A biopsy is usually helpful, and all our patients underwent open biopsy. The histopathology suggestive of ABC shows proliferative fibroblasts, spindle cells, areas of osteoid formation, and an uneven distribution of multinucleated giant cells that tend to surround the fluid-filled cavities in a “pigs at the trough” formation.[11]

There are many variations in the treatment of ABC which include irradiation alone, or a primary surgical approach with or without some kind of adjuvant treatment. Theoretically, adjuvant therapy may consist of systemic chemotherapy, radiotherapy, and physical adjuvants such as phenol, hypertonic saline merthiolate, PMMA cement applied locally, and cryotherapy.[14]

Phenol is a nonselective cytotoxic agent and is usually applied directly to the surface of curetted tumor walls; it kills the remaining residual tumor and normal cells. It is effectively used as a sterilizing agent. The recurrence rate in an ABC after curettage only is 41%, which is seen more in pediatric patients compared to adults.[15] ABCs treated with curettage and adjuncts such as phenol have a recurrence rate of 12.5%–20%.[16]

En bloc resection is indicated for lesions in expendable bones such as metatarsals and tarsals. Such lesions, postresection, have been treated with tricortical iliac crest graft,[17] tibial diaphyseal cortical graft, or nonvascularized fibular autograft.[18]En bloc resection so far has been reported with lowest recurrence rate.[17] In this study, we treated four cases of ABCs with extended curettage using phenol as an adjuvant and reconstruction with nonvascularized fibular strut grafting and osteosynthesis in two patients, and got an average of 5 months for graft consolidation and no signs of recurrence up to the final follow-up of 2 years.

In giant ABCs, preservation of the bone length is important for good function of the affected limb and nearby joints. Patients with large lesions of the distal femur or proximal tibia can be treated by resection and providing mechanical support by autograft, whereas lesions of the foot might be best treated by resection and arthrodesis using autograft.[8] According to our study, such treatment reduces the local recurrence rate considerably as well as reduces disability.

The ideal graft material to be used after curettage should be osteoinductive, osteoconductive, osteogenic, and easily available. Autologous cancellous bone graft is rapidly incorporated, easily re-vascularized, and not immunogenic. The main drawbacks of cancellous bone are a failure rate of up to 48% if used on its own and limited supply for large defects. Another disadvantage of cancellous bone grafting is that the graft does not provide immediate structural strength and necessitates the use of additional mechanical device to prevent fracture.[19]

Nonvascularized autogenous fibula bone grafts are biologically active grafts with relatively low donor site complications that will be replaced completely by living bone and that are capable of remodeling to fulfill the functional needs. Its cortical composition provides immediate stability to the surrounding joints. Fibula as a whole acts as an internal splint, maintaining length with nonvascularized strut graft. To ensure long-term graft incorporation, the fibular cortical grafts which bridge the bone defect after the resection of diaphyseal bone cyst should be securely anchored onto the normal bone with a supplemental form of internal fixation which will promote union of the cortical graft to the host bone.[8]

Vascularized autologous cortical graft is superior to nonvascularized graft but not preferred due to complexity of the procedure, increased operating time, and the need for microsurgical techniques.[20] Bone graft substitutes also offer an alternative choice but they do not offer structural support or integrate well with bone.[20]

Thus, the advantages of the method used in this study are that the autogenous nonvascularized fibula graft has enough strength with minimal need for supplementary fixation and promotes biological consolidation.

Conclusion

Reconstruction of bone cavities in ABC using nonvascularized fibular strut graft is ideal, reliable, safe, and a useful method yielding excellent results. With minimum 2-year follow-up, we did not find recurrence in any case treated with curettage with the use of an adjuvant and fibular strut graft with/without osteosynthesis.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.